After nearly 100 sessions with C.I.A. and F.B.I. interrogators at a heavily guarded, undisclosed location, the captured terrorist Abu Zubaydah has provided information that American officials say is central to the Bush administration's efforts to pre-empt a new wave of attacks against the United States.

The officials say Mr. Zubaydah, a former lieutenant to Osama bin Laden, offered clues that led to the arrest of an American citizen who was accused this week of plotting to detonate a crude radioactive device somewhere in the United States. They said Mr. Zubaydah had also provided vital information, perhaps inadvertently, about the identity of one of the central planners of the Sept. 11 attacks, Khalid Shaikh Mohammed, a Kuwaiti-born extremist and leading operative for Al Qaeda.

Mr. Zubaydah is not considered a cooperating witness. But law enforcement and intelligence officials say that he is talking with American interrogators and that the information he has provided is matched and checked against other evidence collected from Afghanistan and Pakistan as well as intelligence gathered from other terrorist suspects and captured Qaeda members.

Both the Central Intelligence Agency and the Federal Bureau of Investigation are under scrutiny for what critics see as intelligence failures that may have thwarted the possibility of preventing the Sept. 11 attacks.

Bush administration officials said Mr. Zubaydah, who was captured in Pakistan in March and has since been moved to a more secure place overseas, is not being tortured by interrogators from the two agencies. They said he was not allowed access to other Qaeda prisoners. He has also been barred from any contact with the outside world, except when it suits the needs of the interrogators in their psychological gamesmanship with Mr. Zubaydah.

Officials said the American interrogation team, made up of C.I.A. and F.B.I. specialists in extracting information without torture from difficult or reluctant subjects, tries to manipulate Mr. Zubaydah by doing things like feeding him disinformation about the status of other Qaeda leaders or the progress of the American investigation of Sept. 11.

Spokesmen for the two agencies have refused to comment on the interrogation of Mr. Zubaydah.

A Saudi-born Palestinian in his early 30's who was the chief recruiter for Osama bin Laden's terrorist camps, Mr. Zubaydah has remained defiant since his capture outside a safehouse in northern Pakistan in March and has taunted his interrogators from the C.I.A. and F.B.I. with statements of his continued loyalty to Al Qaeda, the officials said.

They said that much of what Mr. Zubaydah had offered in interrogations is believed to have beeen intended to lead investigators astray. His information has prompted the Bush administration, for example, to issue public terrorism alerts involving possible attacks on banks, shopping malls, apartment buildings and landmarks in New York City, including the Brooklyn Bridge and the Statue of Liberty.

Many of the threat warnings based on Mr. Zubaydah's information were later discredited. ''He's cagey, and we certainly don't believe everything he says,'' an American law enforcement official said.

Still, officials said, Mr. Zubaydah has provided valuable information, often without meaning to do so. They said that in his boasting about the terrorist network and its plan to topple the American government with attacks more devastating than those on Sept. 11, he has dropped clues that could be checked against information gathered elsewhere. His clues are sometimes no more than a few cryptic words, a date, or a location.

In the case of the ''dirty bomb'' plot, American officials said, Mr. Zubaydah confirmed the plan's existence and acknowledged that someone had been recruited to oversee the project, in which radioactive material would have been wrapped around a conventional explosive and detonated in the United States. But the American officials said Mr. Zubaydah would not or could not provide a name for the organizer of the attack.

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The C.I.A. and F.B.I. then tried to match Mr. Zubaydah's clues with information from interrogations of other suspects, and with information from notebooks and computer disks seized from Qaeda hideouts in Pakistan and Afghanistan.

Within days, they said, they had identified the plot organizer as Abdullah al-Muhajir, 31, a former Chicago gang member who had met with Mr. Zubaydah in Afghanistan last December. The man, born Jose Padilla, was arrested at O'Hare International Airport in Chicago last month after traveling from Pakistan.

Mr. Zubaydah was arrested with several of his lieutenants, a number of them from Saudi Arabia, in the Pakistani city of Faisalabad, where they had fled in the aftermath of the American assault on Afghanistan.

''People seem to have forgotten that when we picked up Zubaydah, we picked up several of his gang who were living in the same compound in Faisalabad,'' said the American law enforcement official. ''And some of those lieutenants were pretty knowledgeable. If something Zubaydah says matches up with something we hear from one of the lieutenants -- bingo, we move on it.''

A Congressional official said the United States had been reluctant to identify the others arrested in Faisalabad or to publicize their usefulness out of fear that their home countries would demand access to them.

The official said the United States often cross-checked Mr. Zubaydah's information with Ibn al-Shaykh al-Libi, a top paramilitary trainer for Al Qaeda who was captured in Pakistan in January. Until Mr. Zubaydah's arrest, he was the highest-ranking Qaeda leader in custody.

Mr. Zubaydah and Mr. Libi, a Libyan, had worked closely together at Al Qaeda's Khalden terrorist camp in Afghanistan and are believed to share a knowledge of the terrorist network's plans for new attacks.

Mr. Zubaydah was seriously wounded in a shootout with Pakistani police during his capture in Faisalabad, suffering injuries to his groin and thigh and was under sedation while in American custody at a heavily guarded Pakistani air base.

American officials said he was later moved out of Pakistan to another location, where the interrogations began in earnest, and that he had largely recovered from the injuries.

For several years, officials said, Mr. Zubaydah worked closely with Mr. bin Laden in the managing of Al Qaeda's terrorist camps in Afghanistan. From a base in neighboring Pakistan, he vetted potential recruits for the camps, deciding which would be accepted. After training, he assigned them to Qaeda cells elsewhere in the world.